Blowout preventers have long been used in maintaining control of oil and gas wells during drilling. Usually several units are used in one stack. This allows blind rams and different size pipe rams to be available in a single stack. After many uses under pressure blind rams and pipe rams may require that the front packings be changed.
Most pipe rams are now designed to seal on one specific size of drill pipe, tubing, or casing. When drilling conditions require changing pipe sizes, e.g., from a 4 inch to a 31/2 inch drill pipe, standard procedure now is to change the complete set of pipe rams, or change the complete front packings.
Prior blowout preventers have utilized front packings which are removable from the ram. This allows the ram to be used in a variety of applications. In most cases the major portion of the front packing is undamaged but the entire packing is replaced whenever its central pipe sealing portion is damaged.
In prior stripping rams, an arcuate insert of reduced friction material has been used between the upper and lower plates to line the pipe receiving recess. A structure of this type is shown in U.S. Pat. No. 4,323,256.
Another type of insert used in the front face of a ram front packer is the resilient retainer which defines a part of a groove into which a plastic sealant is injected as shown in U.S. Pat. No. 4,227,543.